arXiv subjects

C. -H. Niu

Publications and source records attributed to C. -H. Niu.

3 recordsLinked to original sources

arXiv2025

BASSET: Bandpass-Adaptive Single-pulse SEarch Toolkit -- Optimized Sub-Band Pulse Search Strategies for Faint Narrow-Band FRBs

The existing single-pulse search algorithms for fast radio bursts (FRBs) do not adequately consider the frequency bandpass pattern of the pulse, rendering them incomplete for the relatively narrow-spectrum detection of pulses. We present a new search algorithm for narrow-band pulses to update the existing standard pipeline, Bandpass-Adaptive Single-pulse SEarch Toolkit (BASSET). The BASSET employs a time-frequency correlation analysis to identify and remove the noise involved by the zero-detection frequency band, thereby enhancing the signal-to-noise ratio (SNR) of the pulses. The BASSET algorithm was implemented on the FAST real dataset of FRB 20190520B, resulting in the discovery of additional 79 pulses through reprocessing. The new detection doubles the number of pulses compared to the previously known 75 pulses, bringing the total number of pulses to 154. In conjunction with the pulse calibration and the Markov Chain Monte Carlo (MCMC) simulated injection experiments, this work updates the quantified parameter space of the detection rate. Moreover, a parallel-accelerated version of the BASSET code was provided and evaluated through simulation. BASSET has the capacity of enhancing the detection sensitivity and the SNR of the narrow-band pulses from the existing pipeline, offering high performance and flexible applicability. BASSET not only enhances the completeness of the low-energy narrow-band pulse detection in a more robust mode, but also has the potential to further elucidate the FRB luminosity function at a wider energy scale.

astro-ph.IM↗

arXiv2022

The Large Dispersion and Scattering of FRB 20190520B are Dominated by the Host Galaxy

The repeating FRB 20190520B is localized to a galaxy at $z=0.241$, much closer than expected given its dispersion measure $\rm DM=1205\pm4\ pc\ cm^{-3}$. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy's plasma properties. A sample of 75 bursts detected with the Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delay $τ(1.41\ {\rm GHz})=10.9\pm1.5$ ms, which is attributed to the host galaxy, and a mean scintillation bandwidth $ν_{\rm d}(1.41\ {\rm GHz})=0.21\pm0.01$ MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an H$α$ emission measure (galaxy frame) $\rm EM_s=620$ pc cm$^{-6} \times (T/10^4 {\rm K})^{0.9}$, implying $\rm DM_{\rm Hα}$ of order the value inferred from the FRB DM budget, $\rm DM_h=1121^{+89}_{-138}$ pc cm$^{-3}$ for plasma temperatures greater than the typical value $10^4$ K. Combining $τ$ and $\rm DM_h$ yields a nominal constraint on the scattering amplification from the host galaxy $\tilde{F} G=1.5^{+0.8}_{-0.3}$ (pc$^2$ km)$^{-1/3}$, where $\tilde{F}$ describes turbulent density fluctuations and $G$ represents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry where $τ$ arises from the host galaxy and $Δν_{\rm d}$ from the Milky Way, the implied distance between the FRB source and dominant scattering material is $\lesssim100$ pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using the $τ-\rm DM$ relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way.

astro-ph.HE↗

arXiv2022

A repeating fast radio burst associated with a persistent radio source

The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium, which is assumed to dominate the total extragalactic dispersion. While the host galaxy contributions to dispersion measure (DM) appear to be small for most FRBs, in at least one case there is evidence for an extreme magneto-ionic local environment and a compact persistent radio source. Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific star formation rate at a redshift $z=0.241\pm0.001$. The estimated host galaxy DM $\approx 903^{+72}_{-111}$ pc cm$^{-3}$, nearly an order of magnitude higher than the average of FRB host galaxies, far exceeds the DM contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host galaxy identifications.

astro-ph.HE↗